Dental furnace



Jan. 1, 1929. 1,697,164

' O. A. COLBY I DENTAL FURNACE Filed May 11, 1927 2 Sheets-Sheet 1 WITNESSES: INVENTOR I, ZZ Ora/ Colby BY ATTORNEY Jan. 1, 1929.

o. A. COLBY DENTAL FURNACE Filed May 11, 1927 Fig. 3.

2 Sheets-Sheet 2 WITNESSES: INVENTOR 1/5502 Ora A Colby.

Patented Jan. 1, 1929.

UNITED STATES 1,697,164 PATENT OFFICE.

ORA A. comm, or MANSFIELD, onro, ASSIGNOR T wns'rmenousr. ntncrnrc & MAN- Ur crURme COMPANY, A CORPORATION or PENNSYLVANIA.

DENTAL FURNACE.

Application filed May 11,

My invention relates to furnaces and more particularly to electrical resistance furnaces applicable to dental work and heat treatment of relatively small-articles. I

An object of my invention is to provide in an electrical resistance furnace wherein the resistor is exposed, in the furnace chamber, means for protecting the work being heated from particles scaling oil the resistor.

Another object of my invention is to provide means for controlling the circuit to said resistor element coincident with the operation of the door of said furnace. I A further object is to provide an improved 16 resistor element whereby oxidation and attendant scaling thereof is reduced to a minimum.

In the manufacture and heat treatment of false teeth, bridge work and the like, and

particularly in the glazing thereof, difliculty has been experienced in preventing particles and foreign matter from scaling ofi the resistor and resistor supporting means, and

- dropping upon the work being heated; which difliculty is largely obviated by my lnvent on.

In practicing my invention, I provide in a furnace chamber a resistor element mounted upon the sides, roof and floor thereofand means carried by the roof below said resistor for catching any particles that may fall from said resistor.

The circuit of the resistor is completed through two plugs mounted in the furnace door which cooperate with sockets mounted in the furnace wall and electrically connected in the resistor circuit, whereby,with the door in operative position, the circuit of the resistor is energized. v y

The contacts carried by the furnace door are electrically connected through a fusible circuit-protective device and means are provided to prevent the melted portions of said fusible device from falling upon the work in the furnace chamber.

In the drawings, Figure 1 is a front elevation of a furnace embodying my invention. Fig. 2 is a side view in vertical section on the line II-II of Figure 1.

Fig; 3 is a view,in vertical section on the line III-III of Fig. 2.

Fig. .4 is a schematic showing of the electrical furnace circuit connections. 1

Referring to the drawings, a furnace embodying my. invention is designated broadly as 1 and comprises a sheet metal shell 2 are- 1927. Serial No. 190,551.

uate in lateral section, a metallic bottom plate 4 and east end plates 6 and 8.

The end plates are provided with flanges 10 and 12, respectively, adapted to receive the peripheral edges of the shell 2; and flanges 14 and 16, respectively, upon which the bottom plate 4 is adapted to be supported. Lining the inner surface of shell 2 and restlng upon plate 4 isa body 18 of suitable refractory material forming the floor, side walls and arched roof of a furnace chamber 20, refractory block 22 is received between the shell 2 and plate 4, adjacent the plate 8 and forms the rear end wall of the furnace chamber.

The front wall of the furnace chamber comprises a block 24 of refractory material which is fitted with the refractory lining 18 and is in face-to-face relation with the front end plate 6 to form the front wall of the furnace chamber. The block 24 is formed with a depending portion 26, for a purpose hereinafter described, which projects downwardly through an opening in the plate 4 between flanges 28 and with the lower edge thereof resting upon a flange 30 formed integral with end plate 6.

An opening is formed in the refractory block 24 communicating with the furnace chamber 20 to afford access thereto and to permit the charging and removing of articles to be heated.

A plurality of rods 32 extend through the furnace body, parallel to the longitudinal axis thereof and are provided with screw-threaded ends extending through the end plates 6 and 8, and are engaged by suitable nuts to clamp the assembly together. The assembly is supported upon suitable logs, cast integral with the plates 6 and 12, which are apertured for the reception of securing bolts or screws (not shown).

The floor, roof and side walls of said furnace chamber are lined with a suitable refractory 34, porcelain in the present instance, molded to provide a plurality of parallel, longitudinally extending overhung grooves 36, for the reception of resistance heating element 38 therein.

The heating element 38 comprises a helically wound metallic resistor threaded through the grooves in the refractory .lining 34, and in order to minimize the oxidation and consequent scaling of the resistor, it is preferably chromiumor nickel-plate.

The resistor supporting lining 34 is enlarged, as at 40 between certain of the resistor receiving grooves in the roof of the furnace and is grooved to accommodate flanges 42 of a refractory plate 44 which is support-ed thereby beneath the over-head portions of the resistor, and substantially co-extensive in length therewith so that particles falling from the resistor and adjacent roof portions are caught thereupon. The portions of the resistor in the side walls of the chamber are so deeply set in the grooves 36 that any particles falling from the resistor will be retained therein.

Upon the floor of the furnace chamber is a work supporting plate 46 supported by portions of the resistor retaining block 34 above theresistor convolutions. The plate 46 is of suitable refractory material such as porcelain. I

The resistor is formed in two sections as indicated in Fig. 4 with one terminal of each section connected to terminals 48 in a terminal box 50 carried by the outer face of plate 12, as shown more particularly in Fig. 2. Current is supplied to the terminals48 through the usual leads 52 connected to a.

suitable source of power (not shown).

The remaining terminals of the two resistor elements are electrically connected to two sockets 54 embedded in the portion 26 of block 24 with the open ends thereof substantially flush with the outer face of block 24, and are adapted to receive contact plugs therein as hereinafter described.

The terminals of sockets 54 project beyond the rear face of block 26 to facilitate making the necessary electrical connections and are enclosed in a terminal box formed by a plate 55 removably secured to flanges 28.

The opening in block 24, affording access to the furnace chamber, is closed by a door removably supported upon a flange 56, formed integral with the front face of plate 6.

The door of the furnace comprises a Inc-- tallic plate 57, and a substantially annular plate 58 secured to the periphery thereof by any suitable means, such as machine screws 59 engaging screw threaded lugs on plate 58. A block 60 of refractory material is positioned between plate 58 and the inturned lower edge of plate 57, and is maintained in spaced relation with plate 57 by spacing members 62 carried by plate 57.

The space between the refractory plate 60 and the plate 57 is filledwith a suitable heat insulating material, such as mineral wool 63.

In the lower portion of the refractory plate 60, and projecting beyond the outer face thereof, are contact plugs 64 in alinement with the sockets 54 mounted in the front wall of the furnace proper. The plugs extend through the plate 60 and at the rear ends thereo are connected to conductor strips 66.

The strips extend over the rear face of plate 60 and are connected to contact sockets 68 which project through plate 60 substantially in alinement with the furnace chamber openmg.

The contact sockets 68 are electrically connected by means of a gold fuse 7 0 electrically secured to thesockets in any suit-able mannor, as by machine screws 71. The position of the fuse is such that when the door is in operative position the fuse is exposed in the furnace chamber and is therefore responsive to the furnace chamber temperature conditions as well as over-load-conditions in the resistor circuit.

Upon the outer face of plate 60, surrounding fuse 70 and substantially co-extensive with the furnace chamber opening in block 24, is formed an arcuate flange 72 and a horizontally extending flange'74 connecting the ends of flange 72.

Manipulation of the door to close or open the furnace is facilitated by a handle 76 of suitable heat insulating material secured to the outer face of plate 57 by angle brackets 7 8;

In operation with the furnace body assembled as above described, and switch (Fig. 4) in circuit-closing position, the door is moved into position to close the chamber with the flanges 72 and 74 substantially filling the furnace chamber opening. With the door in this position the contact plugs 64 carried thereby are received in sockets 54, thereby completing a circuit extending through the resistor andgold fuse 70.

Energization of the resistor causes the furnace to heat up, and after a period of about twenty-five (25) minutes the furnace chamber attains a temperature of approximately 1950 F. The fuse 70 is so proportioned that it melts at the temperature of 1950 F. and, by means of instrumentalities well-known in the art, an indication of said melting is given.

The door is then removed, a new fuse connected in the circuit, the work to be heated placed in the chamber and the door replaced effecting the re-energization of the resistor.

The temperature will drop to about 1650 F. duringthis replacement of the fuse and the introduction of the work. The time necessary to again reach a temperature of 1950 F. is approximately eight (8) minutes, this being the time necessary for the enamel on the work to become properly heat-treated at those temperatures. As soon as the temperature of 1950 F. has again been reached the fuse will operate to interrupt the circuit of the heating unit and a suitable indicating device may be used to notify the operator that the operation has been completed.

By my invention I have provided an electrical resistor furnace with improved circuit controlling and protective means, and wherein contamination of the work being heated by particles falling from the resistor is reduced to a minimum.

It is obvious that many changes of construction may be restorted to and still be within the scope of the present invention. For example, the shape and proportions of the furnace structure may be varied considerably, and with suitable electrical connections a multiphase power supply may be employed instead of the single phase supply shown. Also a covered work-supporting plate may be used to protect the articles being heated, instead of the protecting plate 44, and the plate 44 may be supported in other ways instead of by the portions 40 of the resistor supporting block 54.

Various modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations be placed thereon as are imposed by the prior art and set forth in the appended claims.

I claim as my invention:

1. In an electric furnace, the combination with a furnace chamber a roof member and resistor-supporting means formed in theroof thereof, of means supported by certain of said resistor-supporting means for preventing the dropping of particles from said resistor and adjacent roof portions upon the work which is being heated.

2. In an electric furnace, the combination with a'furnace chamber, side-walls and a roof member, and resistor-receiving grooves in the roof and walls thereof, of means carried by said roof, beneath said grooves to prevent the dropping of particles from said resistor upon the work which is being heated.

3. In an electric furnace, the combination with a furnace chamber and resistor-receiving grooves in the roof and walls thereof, of means carried by said roof, beneath said grooves, to prevent the dropping of particles from said resistor upon the work which is being heated, said means comprising a plate of refractory material substantially co-extensive with the roof area of said chamber.

In testimony whereof, I have hereunto subscribed my name this 29 day of April, 1927.

ORA A. COLBY. 

